Understanding an object is sufficient in that the object itself forms a department of the experience of the object. This certainly fails when the object is an other, an alter-ego, when the object has a hidden side which can never be known. An other subject is unknowable in principle, by the very nature of the subjectivity that is your own, unlike the merely contingent hidden side of objects that are or can be understood. Mind or consciousness as experienced here is inseparable from the striving to master this problem, to get outside of itself in a way that breaks down the barrier of other subjectivity. Everything that goes on in one way or another answers to this without ever succeeding. There is instead a continual divergence, endlessly branching detours, all of thought, in the name of an impossible and apocalytptic convergence.